The present invention relates to a copper clad laminate excellent in hole processability in laser beam drilling which provides efficient formation of an via-hole in a printed circuit board.
Recently, with the increasing wiring density, the laser beam drilling, which allows a finer processing than the conventional mechanical drilling, has been used more frequently in the production of electronic components and wiring boards both utilizing copper foil as a conductor.
However, when drilling a hole in a copper foil surface by illuminating the same with the carbon dioxide laser beam excellent in general-purpose properties, the reflectance of copper reaches almost 100% at the wavelengths of the carbon dioxide laser beam, that is, around 10 xcexcm, leading to a problem of extremely low laser processing efficiency.
In order to offset such a decrease in processing efficiency, a high output carbon dioxide laser drilling machine is required; however, when performing laser processing with high energy of such a high output carbon dioxide laser drilling machine, the resin board subjected to drilling simultaneously with the copper foil is drilled to excess and damaged, which gives rise to a problem of being unable to drill a hole of intended shape.
Further, the amount of the splashed matter accompanying the laser processing becomes larger, which causes another problem of, for example, contamination of the laser drilling machine as well as the non-processed portion of the material having been subjected to the processing.
So, in order to avoid these problems, an attempt has been made to first make a hole in the copper foil portion by the chemical etching and then drill the resin portion by the laser beam. In this case, however, the number of the processes becomes larger than that of the case where the copper foil and the resin portion are drilled at a time, causing an increase in costs. Thus, this attempt also has a disadvantage.
On the other hand, as means for laser-processing a metal exhibiting a high reflectance at the laser beam wavelengths, a method has generally been adopted in which the surface of the metal is provided with a material with high absorptivity, so as to allow the material to absorb the laser beam and generate heat, and with the heat the metal is processed. Further, it has been known that roughing the material surface also allows a high processing efficiency.
Further, there has been proposed a method in which the surface of the copper foil is subjected to oxide treatment (black oxide treatment method) at the time of drilling, in order to increase the processing efficiency.
How ver, with any of the above proposals, the operations and treatments become complicated, and a sufficient laser processing efficiency cannot be obtained, considering how complicated they are. In addition, in the copper foil provided with the above-described surface treatment layer, the treatment layer tends to peel off since it is quite brittle and become a contamination source during the processing, which gives rise to another problem.
Further, there has been proposed a method in which copper foil itself is made thin so that it can be drilled by a low energy laser beam. However, since the thickness of the copper foil actually used varies from 9 xcexcm to 36 xcexcm, the copper foil can be made thin only for some cases. Furthermore, in order to perform drilling under such low energy conditions, the copper foil required to be as extremely thin as 3 to 5 xcexcm, which causes another problem of handling etc.
As described so far, although there has been proposed several methods of improving the copper foil in current use, the present situation is that any of the methods is not satisfactory for the laser beam drilling, in other words, the copper foil materials suitable for the laser processing have not been obtained yet.
The present invention has been made in light of the above-described problems. Accordingly, the object of the present invention is to provide a copper clad laminate which makes the laser beam drilling extremely easy and is suitable for forming an interlayer connection microhole by improving the surface of its copper foil, which is to be used as the surface which the laser beam enters, in the production of printed circuit boards.
The present invention provides:
1. a copper clad laminate including an electrodeposited copper foil for use in laser beam drilling, characterized in that a matte side of the above electrodeposited copper foil which has become the electrolyte side at the time of electro-deposition is used as a surface which a laser beam enters;
2. the copper clad laminate according to the above description 1, characterized in that a surface roughness Rz of the matte side of the above electrodeposited copper foil is 2.0 xcexcm or more;
3. the copper clad laminate according to the above description 1 or 2, characterized in that the matte side of the above electrodeposited copper foil is subjected to additional roughening treatment by the electrodeposition;
4. the copper clad laminate according to any one of the above descriptions 1, 2 and 3, characterized in that a shinny side of the above electrodeposited copper foil is subjected to roughening treatment by electrodeposition; and
5. the copper clad laminate according to the above description 3, characterized in that roughening treatment is performed using any one or more of Ni, Co, Sn, Zn, In and alloys thereof as metals for use in the electrodeposition.